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[require] GLSL >= 1.10 [vertex shader] void main() { gl_Position = gl_Vertex; } [fragment shader] uniform float v; void main() { gl_FragColor = v + vec4(0.0); } [test] uniform float v 0.5 draw rect -1 -1 2 2 probe all rgba 0.5 0.5 0.5 0.5